Nicotine exposure in utero appears to shut down a stress reaction that normally helps newborns survive low-oxygen conditions, according to a new study using an animal model of sudden infant death syndrome.
Researchers at Duke University in Durham, N.C., exposed pregnant rats to nicotine and then placed their day-old offspring in a lowoxygen environment, similar to that of a human infant whose breath is blocked by a pillow.
They found that one-third of the baby rats died for lack of the stress reaction mechanism, a hormone that governs heartbeat and blood flow in response to low oxygen.
It has long been known through epidemiological studies that cigarette smoke is the strongest risk factor for SIDS, a term describing sudden unexplained death in children under 1 year of age. There are about 8,000 such deaths a year.
Theodore Slotkin and his colleagues at Duke believe their study could explain how smoking during pregnancy increases SIDS risk.
“We believe this is the same mechanism that operates in humans,” said Slotkin, a professor of pharmacology, neurobiology and psychiatry. “I just hope that this information will dissuade mothers from smoking” and from using nicotine patches.
Slotkin’s studies have shown that the stress hormones, produced by the adrenal glands, are important to the developing fetus and in the first year of life. If oxygen is low, the hormones are used to redistribute blood flow in the brain and heart, and to maintain cardiac rhythm.
But nicotine exposure in utero interferes with these special systems, Slotkin said, so that they shut down too soon.
In addition, he said, being able to tolerate low oxygen is especially important during the birthing process, so the same nicotine effect could explain the fact that the infants of women who smoke are more likely to die during delivery.